Fluid-powered impact vibrators, such as hydraulic hammers, may be used for crushing rock, concrete or other building materials, and may be provided as accessory parts or attachments for a carrier machine, such as excavators, loaders or other construction machines.
Hydraulic hammers generally comprise a percussion piston arranged for reciprocating movement within a cylinder housing by controlled hydraulic fluid pressure. The piston drives a work tool such as a chisel, blade or rock breaking bit.
Typically an impact vibrator may be attached to the jib of a fluid-powered excavator or other carrier machine, and may be connected via a fluid pressure inlet line as well as a return flow line to the hydraulic fluid supply unit for the fluid-powered excavator. The fluid pressure inlet line provides hydraulic fluid at high pressure while the return flow line is a low pressure region.
The percussive piston movement in the operating stroke direction or in the opposite, return stroke direction may be affected by a piston control valve that is associated with or integrated into the hydraulic hammer. In particular, the control valve can include a spool valve acting upon two annular percussion piston surfaces of different size, which are located in opposite movement direction, such that the smaller annular surface (effective in the return stroke direction) is always connected to the input pressure line, and the larger annular surface (effective in the operating stroke direction) is connected via the spool valve alternately to the fluid pressure inlet line and the return flow line.
The hydraulic fluid supplied by the carrier machine is designed for the internal power demands of the carrier machine itself, and is not always at an optimum pressure or flow rate for an attached hydraulic tool. Excessive fluid flow from the carrier machine, excessive back pressure from a poor hydraulic kit installation on the carrier machine, or an incorrectly adjusted control valve on the hydraulic hammer can each result in a hydraulic hammer being operated using a hydraulic pressure greater than that specified for the hydraulic hammer.
It is known to provide a pressure-limiting valve in conjunction with the piston control valve, so that when the pressure in the fluid pressure inlet line exceeds a predetermined maximum pressure, the pressure-limiting valve causes the piston control valve to the operating stroke position, thereby stopping operation of the hydraulic hammer. However the piston control valve remains in the operating stroke position only as long as the pressure in the fluid pressure inlet line exceeds the predetermined maximum pressure. When the pressure in the fluid pressure inlet line is reduced below the predetermined maximum pressure the piston control valve is free to return to the return stroke position, thereby resuming operation of the hydraulic hammer. This may result in uncontrolled restarting of the operation of the hydraulic hammer.
The present disclosure is directed to overcoming one or more of the problems as set forth above.